I don't have your table names or descrpitions so I cannot post an exact answer.

You need to match up the number of columns in the table with the number of columns in the select.

If the table has 3 columns, the select needs 3 columns, etc...

It is also a good idea to specify the column names in the insert side as well:
insert into table3(s_no,some_date,name,phone)
(select S_No, sysdate, Name, Phone from table1 A where not exists (select row1 from table2 B where A.row1=B.row1));